by Nigel Cliffe , from a design by Peter Clark
© 1996, Nigel Cliffe and the 2mm Scale Association.
Introduction
Another page describes the fonly drilling machine. In some respects that article was a prelude to the machine described below. The lathe is an accurate machine, capable of precision work to better than 0.05mm (0.1mm on diameter). This is sufficient for most 2mm Scale models (and N scale). It is also suitable for small components in HO/OO scales.
The spirit of the fonly family is to adapt ideas to the machine as they are needed. There is no "right" way to build the lathe, nor is there a definitive set of accessories. Instead, there are a few principles which underlie the machine and one builds parts as needed, copying principles from other machines. With this in mind, I plan to explain only the basic components. In the first part, the bed, headstock, drilling tailstock and hand turning tool will be described. In the second, cross slide, depth stop, taper turning attachment, tailstock steady and flycutter will be added, along with photographs of some of the other accessories. With the components described it is possible to produce small turnings such as boiler fittings and buffers. Wheels can be produced, though it isn't the ideal machine for repetitive work.
The lathe can be built in a weekend, indeed, one was built by Peter Clark under the gaze of the public during a day of the IMREX model show, starting at 10am, with the machine cutting metal by 6pm.
Photograph by Peter Clark.
Principles
In common with the drilling machine, the power for the lathe is provided by a minidrill. The examples built by Peter Clark and the author have all used Minicraft Buffalo models, with both old and new body designs. The longer parallel front bearing of the old model makes construction a little easier, however the bearings in the newer model appear to be more substantial. The drill is held by two wood supports, the rearmost having oversized location holes which allow for adjustment of the axis of the finished lathe. By designing in the adjustment, the components need only be made to moderate accuracy, and the precision comes with final adjustment.
The lathe has a flat bed made from a piece of steel plate to a stable wooden base. The lathe tools are made with wooden bases, and slide over the metal bed. Experience has shown that birch ply slides easily over a mild steel base, and that, provided reasonable cleanliness is observed, the sliding action will not mark the bed in any detrimental manner.
The hand held tool holders are derived from those which were available for the old Lorch watchmaker's lathes. With the small sizes of workpieces, the fine control available with direct hand control is often preferable to the control available on the screw advance of a more conventional machine. The tool holders feature an ingenious "three legged stool" which allows for very easy adjustment of tool height.
The tailstock drill chuck is propelled by hand. Originally a lever feed was fitted, but experience has shown that this is an unnecessary feature. The photograph shows a parallel and taper turning advance fitted to the rear of the bed. This accessory allows the hand turning tools to finish work to a known, constant, diameter, or to turn tapers of known angle.
Extra components which can be built include; fixed tailstock centre, fixed steady (to support long work such as a boiler), frame drilling component, fly cutter and light milling attachment (eg. for cutting the scallop out of the base of chimneys and domes), large diameter work holder, sanding and grinding table.
By using the standard minicraft accessories, round bar up to 6mm diameter and square up to 2mm (using the collets). By the addition of extra components (which can be made on the machine), items up to 10mm diameter can be held. Parts, Materials and Tools.
In the article on the drilling machine, the merits of various mini-drills were discussed. For the lathe it is essential that a drill with substantial bearings is used as lateral loads will be applied when turning. The Minicraft Buffalo (MB1010) has proved ideal, though models by Proxxon and Dremel may also be suitable. Recently Minicraft have discontinued the 6mm chuck on the MB1010, though the 3.2mm version remains in production. Older versions should be available in shops for some time.
Types of plywood were described in the earlier article. The drilling machine comes in handy during construction, so why not make that one first? The construction often bolts items together. Unless stated, don't glue things together, you may need to take it apart to add an additional feature at a later date.
The only special tool required during construction is a M3 tap (or 6BA), with a suitable tap holder. Get a taper or second tap, and buy a quality item - only one is needed, not the set!
In addition to wood, metal, screws, nuts and bolts, the lathe requires tool steel and a small 3 jaw drill chuck mounted on a mandrel. Look for suppliers in the model engineering press or at the larger model shows. I have bought chucks, taps and tool steel from Shestos in the past.
As always, take care when making and using the machine, hold material in a vice, use files with handles and eye protection when operating machine tools.
The Lathe Headstock and Bed
Components:
Plywood in 18mm (0.75in) and 9mm (0.375in) thickness. 3mm (0.125in) steel plate. Various M6 and M4 nuts and bolts, woodscrews, washers.
Plans:
Assembly:
Cut out the wooden base, support and metal bed. The two long sides of the metal bed should be parallel. The bed support is a little smaller than the bed, it is overhung on all sides. Mark out the holes. Note that part of the bed has to carry the tailstock support, and bear this in mind when marking the holes. Drill all the holes, countersinking those on the bed. Make sure that the countersunk screws are below the surface of the bed when assembled. The hex nuts are pressed into the ply base. The nut cuts a hexagonal hole as it is drawn into the ply. Open the 4mm hole to about 7mm, and pull the nut into the hole using a bolt, with the load supported by a suitable washer.
Assemble the bed, bed support and base (figure 3 shows assembly of bed and headstock supports).
Mark out and cut out the two bearing supports for the drill. If using a drill other than the Mini-craft Buffalo, adjust the two large holes, and spacing between the supports to suit. The two bearing supports for the drill do not need to be precisely round. If they are cut carefully, they will work as long as they can be firmly clamped on the drill. The rear support is tightened to just lightly grip the drill, the front support is clamped tightly. The two screw holes to attach the rear support are drilled oversize to allow for adjustment of the machine at a later stage. Use washers on these holes during assembly. Fit the front bearing support, and clamp the drill into the lathe. Fit the rear bearing support and loosely screw onto the base.
Setting up:
Insert a length of true round bar into the drill chuck. Bar can be tested for truth by rolling on a piece of glass, looking to see if it ceases contact at any point, or has a preferential position that it rolls to. Use the largest diameter that your chuck can hold.
Adjust the rear carrier until the test bar is horizontal with respect to the lathe bed (figure 4). This can be done with a pointed implement set horizontally in a tool holder. Use the point to trap a flat shim of metal against the side of the test bar. If the shim stands vertically at various positions along the test bar, then the lathe is horizontal with respect to the bed.
Next, adjust the test bar so it is parallel to the lathe bed sides. Use the same pointed tool, adjusted so that the toolholder rests along the reference edge of the bed.
Re-check both settings before use.
Tailstock
Tailstock on lathe bed. Peter Clark
Components
tailstock guide, 3mm and 1.5mm steel (0.125 and 00625in). tailstock base piece, 12mm ply (0.5in) tailstock body piece, either a cube of softwood, or a ply sandwich. chuck on mandrel from a tool supplier. 2 M3 screws and washers, countersunk woodscrews.
Assembly
There are two pieces of metal to make up the tailstock guide. The lower piece undercuts the upper to ensure that the tailstock is guided along its side, not bottom corner.
Tailstock Drill
Drill 4mm holes through the two pieces of tailstock guide (oversize for adjustment). Drill tapping holes in the bed, and tap M3. Use two M3 screws with washers to assemble (figure 6). Check that the inner edge of the guide is parallel to the axis of the lathe.
The tailstock is made from two pieces of wood fixed together with three wood screws (figure 7).
Measure the diameter of the tailstock chuck mandrel. Put a medium sized
drill (say 4mm) in the headstock, and use it to drill a hole in the
tailstock (figure 8). Increase the size of the drill to that of the
mandrel in stages. This guarantees that the tailstock is correctly centred
and parallel to the headstock.
The tailstock chuck can either be fixed with Aradite, or the tailstock base can be slit with a saw (on the side marked with one fixing screw) and the mandrel held by tightening the fixing screw.
Tool Holder
The basic tool holder is designed for hand turning, though with the addition of depth stops and slides (to be described in the next instalment) machine turning is achieved.
The tool is adjusted for centre height and rake on the "three legged stool" of three M3 grub screws which supports the tool holder. Brass is the easiest material to machine, but steel or aluminium will work equally well. The M5 bolt clamps the tool tightly to the base piece after adjustment (figure 9).
Components:
Base 12mm (0.5in) ply. M5 nut and bolt. M6 washer. Tool holder blank (brass, steel or aluminium) 8 by 16 by 18mm (0.375 by 0.7 by 0.75in). 4 x M3 grub screws Tool steel - 4mm round blanks
Construction:
Cut out the base, and drill a 5mm clearance hole. After counterboring to suit the nut, crush a nut into the lower side of the base. Cut a chamfer on the edge of the base. The chamfer ensures that the work piece in the lathe clears the base, and that the load on the tool tip is transmitted into the base, rather than tipping the tool holder forwards (figure 10).
Cut out the tool holder blank, and drill the holes indicated - one 5mm clearance, four M3 tapping and one 4mm clearance (figure 11). It can be useful to open half of the M3 hole to 3mm clearance, rather than tapping the entire length. Tap the four M3 holes, and assemble.
It is necessary to grind toolsteel to make a cutting tool. To begin with, try to make two tools, one with a sharp corner, the other with a rounded face (figure 12). These can be ground using a grinding disk in the mini-drill, whilst holding the tool steel blank in a medium pin vice. For more details consult a model engineering text book, eg, The Amateur's Lathe by L.H.Sparey.
Grind a tool to shape, and fit into the holder. Use the three grub screws to adjust the tool to centre height, then tighten the centre M5 bolt.
Using the lathe
Having made all the parts described above, the basic lathe can be put to some use making components.
In Part 2, I will describe some accessories which can accompany the basic machine.
